The present invention relates to a pneumatic tire reinforced by steel cords, and particularly relates to a pneumatic tire for a motor vehicle, in which the cut-off ends of steel cords are caused to adhere to rubber well enough to enhance the durability of the tire.
In a conventional pneumatic tire for a motor vehicle, a reinforcing layer of steel cords is embedded in rubber for a carcass, a belt, a chafer or the like. Since the modulus of elasticity of the steel cords is very high, the steel cords embedded in the rubber act to suppress the deformation of the tire. However, since the difference between the modulus of elasticity of steel cords and that of the rubber is large, there is a drawback that a shearing force acts to the mutually stuck surfaces of the rubber and each of the steel cords in the longitudinal direction of the steel cord to separate the mutually stuck surfaces from each other. For that reason, the steel cord is plated with brass to heighten the sticking power between the rubber and the steel cord.
Since the element wires of each of the steel cords, which are embedded in the rubber of the conventional pneumatic tire, are plated with the brass except the cut-off ends of the element wires, the sticking power between the rubber and each of the element wires is heightened so that the rubber and the element wire are prevented from being separated from each other. However, since the cut-off ends of the element wires are not plated with the brass and are gathered to form a plane, the sticking power between the rubber and the cut-off ends is very low so that the rubber and each of the cut-off ends are likely to be separated from each other. Besides, since the difference between the modulus of elasticity of the rubber and that of the steel cords is large, as mentioned above, a local large strain is likely to be caused in the rubber at the cut-off end of each of the element wires to partially crack the rubber. Therefore, there is a problem that if such strain is repeatedly caused, the rubber is separated from the cut-off end portion of each of the steel cords in a short period of tiem.
It was disclosed in the Japanese Patent Application No. 28882/80 now Japanese patent No. 55-28882 that the ends of the element wires of each of steel cords are dispersed as a bamboo broom to heighten the sticking power between rubber and each of the ends of the element wires. In that case, however, troublesome work such as reducing the ratio of formation of the steel cords and increasing the twisting pitch on the steel cords needs to be done.